1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate. In particular, the present invention relates to a semiconductor substrate which is obtained by bonding a single-crystalline semiconductor layer or a polycrystalline semiconductor layer to a substrate having an insulating surface. In addition, the present invention relates to a semiconductor device using the semiconductor substrate.
2. Description of the Related Art
Integrated circuits have been developed, which use a semiconductor substrate called a silicon-on-insulator (SOI) substrate that has a thin single-crystalline semiconductor layer over an insulating surface, instead of a silicon wafer that is manufactured by thinly slicing an ingot of a single-crystalline semiconductor. The integrated circuits using an SOI substrate have attracted attention as an integrated circuit which reduces parasitic capacitance between a drain of a transistor and the substrate and improves the performance of a semiconductor integrated circuit.
As a method for manufacturing an SOI substrate, a hydrogen ion implantation separation method is known (for example, see Reference 1: U.S. Pat. No. 6,372,609). The hydrogen ion implantation separation method is a method in which, after an oxide film is formed over a surface of a silicon wafer by a thermal oxidation method or the like, hydrogen ions are implanted into the silicon wafer from the surface to form a microbubble layer at a predetermined depth from the surface, and a thin silicon layer (SOI layer) is bonded to another silicon wafer using the microbubble layer as a cleavage plane. In addition to heat treatment for separating the SOI layer, it is necessary to perform heat treatment in an oxidizing atmosphere to form an oxide film on the SOI layer and perform heat treatment at 1000° C. to 1300° C. in a reducing atmosphere to increase the bond strength after removing the oxide film.
As one of examples of an SOI substrate in which an SOI layer is formed over a glass substrate, a structure is known in which a thin film of single-crystalline silicon having a covering film is formed over a glass substrate having a coating film by a hydrogen ion implantation separation method (see Reference 2: Japanese Published Patent Application No. 2004-134675). In this case also, the thin silicon layer (SOI layer) is formed over the glass substrate in such a way that a microbubble layer is formed at a predetermined depth from the surface by implantation of hydrogen ions to a single-crystalline silicon wafer, the glass substrate and the single-crystalline silicon wafer are bonded to each other, and the silicon wafer is separated using the microbubble layer as a cleavage plane.